A channel quality indicator (“CQI” for short) and a sounding reference signal (“SRS” for short) that are sent by a user equipment (“UE” for short) to a base station may be collectively referred to as an uplink signal. The base station can obtain states of uplink and downlink channels of the UE according to an uplink signal sent by the user equipment, and help schedule uplink and downlink data of the UE to a proper channel resource for sending. When the UE needs to send an uplink signal to a cell of the base station, the UE needs to obtain uplink signal configuration. Therefore, the base station needs to send uplink signal configuration information to the UE to notify the UE of a period and a time-frequency resource for sending the uplink signal. In addition, the UE needs to obtain timing advance (“TA” for short) relative to the cell. Therefore, the base station needs to send a timing advance command (“TAC” for short) to the UE, so as to help the UE determine and adjust the TA.
TA of a particular UE relative to a particular cell varies with factors such as a location of the UE and a size of the cell. Therefore, the UE starts or restarts a time alignment timer (“TAT” for short) each time the UE obtains a TAC from the base station, and when the TAT expires, the UE considers that a TA value corresponding to the TAC is no longer valid. To prevent uplink interference, the UE terminates transmission of all uplink signals except a random access request, and releases the uplink signal configuration, so that the base station reuses all or some of resources indicated by the uplink signal configuration, so as to improve utilization efficiency of uplink resources. Later, when uplink data arrives, the UE initiates a contention-based random access procedure to the base station, and obtains a TAC in this process to make the UE restart the TAT, the base station sends uplink signal reconfiguration information to the UE, and then the UE begins sending an uplink signal to the base station; when downlink data arrives, the base station also needs to send uplink signal reconfiguration information and a TAC to the UE, so that the UE begins sending an uplink signal and performs uplink and downlink data transmission.
However, when there are relatively few users in the cell, after the UE releases the uplink signal configuration, the base station may not reuse resources indicated by the uplink signal configuration for another UE, but when uplink data or downlink data arrives, the base station still needs to send reconfiguration information to the UE, so as to resend the previous uplink signal configuration to the UE. Redundant signaling means a longer control delay, which delays sending of uplink and downlink data, and degrades user experience. Furthermore, when a cell is small enough, regardless of a location of the UE in the cell, TA of the UE relative to the cell is zero; in this case, a TAC obtained by the UE during a random access procedure or actively sent by the base station is definitely zero, but the UE still needs to perform the random access procedure.
The random access procedure is a relatively tedious and time-consuming process, which also delays sending of uplink and downlink data, and degrades user experience. In addition, in some cases, for example, the cell is small enough or the UE is still for a long time, TA of the UE relative to the cell may not need to be adjusted in a relatively long time, and therefore, relatively long timing duration of the TAT may be set. In this case, the TAT can hardly expire. As long as the TAT does not expire, no matter whether uplink and downlink data needs to be sent, the UE sends an uplink signal to the base station according to uplink signal configuration. The uplink signal is useless, and sending the useless uplink signal wastes valuable battery power of the UE. In this case, merely setting a relatively short TAT increases signaling overheads for maintaining the TAT, and causes the TAT to expire more easily. As a result, the foregoing two disadvantages become more serious.
Therefore, in some cases of the prior art, the random access procedure or uplink signal reconfiguration is unnecessary, and a useless uplink signal is sent. Sending of the unnecessary control signaling and the useless uplink signal delays sending of uplink and downlink data, wastes system overheads and power of the user equipment, and degrades user experience.